GDP

I'm tracking down a problem where in GDP/JavaScript interface where debug flags are not preserved and ran across a problem where linking fails under Darwin with shared libraries.

The solution is that under Darwin, either we use create libgdp.0.7.dylib or run

 install_name_tool -id libgdp.0.7.dylib libs/libgdp.0.7.dylib 

Here's my setup inside the gdp tree:

bash-3.2$ cd test
bash-3.2$ ls ../libs
libep.3.0.dylib         libgdp.0.7.dylib        makelinks.sh
libep.a                 libgdp.a
libep.dylib             libgdp.dylib

In the above note that libgdp.0.7.dylib is in the libs/ directory.

Here's a small test case, where we set the debug file and then get it:

bash-3.2$ cat epTest.c
#include <stdio.h>
#include <ep.h>
#include <ep_dbg.h>

int main(int argc, char **argv) {
  FILE *fp = fopen("foo.txt", "w");
  ep_dbg_setfile(fp);
  printf("ep_dbg_getfile(): %p\n", ep_dbg_getfile());
}
bash-3.2$ cc -I ../ep/ -Wl,-rpath,/Users/cxh/ptII/vendors/gdp/gdp/libs -I .. epTest.c -L ../libs -lgdp.0.7

Sadly, Darwin does not have ldd, we have to use otool to see what dependencies we have.

bash-3.2$ otool -L a.out
a.out:
        libgdp.so.0.7 (compatibility version 0.0.0, current version 0.0.0)
        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1226.10.1)

In the above, note that the binary was created with a dependency on libgdp.so.0.7 instead of libgdp.0.7.dylib

bash-3.2$ ./a.out
dyld: Library not loaded: libgdp.so.0.7
  Referenced from: /Users/cxh/ptII/vendors/gdp/gdp/test/./a.out
  Reason: image not found
Trace/BPT trap: 5
bash-3.2$ 

In the above, the binary does not run.

However, if we copy the shared library to libgdp.so.0.7, then it works!

bash-3.2$ cp ../libs/libgdp.0.7.dylib ../libs/libgdp.so.0.7
bash-3.2$ otool -L a.out
a.out:
        libgdp.so.0.7 (compatibility version 0.0.0, current version 0.0.0)
        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1226.10.1)
bash-3.2$ ./a.out
ep_dbg_getfile(): 0x7fff7082b050
bash-3.2$ 

One possible solution is to have the Makefile generate libgdp.0.7.dylib.

Another possibility is to use the Mac install_name_tool:

bash-3.2$ rm ../libs/libgdp.so.0.7
bash-3.2$ install_name_tool -change libgdp.so.0.7 libgdp.0.7.dylib a.out
bash-3.2$ otool -L a.out
a.out:
        libgdp.0.7.dylib (compatibility version 0.0.0, current version 0.0.0)
        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1226.10.1)
bash-3.2$ ./a.out
ep_dbg_getfile(): 0x7fff7082b050
bash-3.2$ 

It would be nice if there was a command to update the LC_ID_DYLIB in the shared library. To see the value of LC_ID_DYLIB:

bash-3.2$ otool -l ../libs/libgdp.0.7.dylib
....
Load command 3
          cmd LC_ID_DYLIB
      cmdsize 40
         name libgdp.so.0.7 (offset 24)
   time stamp 1 Wed Dec 31 16:00:01 1969
      current version 0.0.0
compatibility version 0.0.0
...

It looks like install_name_tool -id will work, see http://stackoverflow.com/questions/33991581/install-name-tool-to-update-a-executable-to-search-for-dylib-in-mac-os-x

To replicate, clean the gdp with (cd ..; make clean; make all_noavahi), then:

bash-3.2$ cd test
bash-3.2$ install_name_tool -id libgdp.0.7.dylib ../libs/libgdp.0.7.dylib 
bash-3.2$ cc -I ../ep/ -Wl,-rpath,/Users/cxh/ptII/vendors/gdp/gdp/libs -I .. epTest.c -L ../libs -\
lgdp.0.7
cc -I ../ep/ -Wl,-rpath,/Users/cxh/ptII/vendors/gdp/gdp/libs -I .. epTest.c -L ../libs -lgdp.0.7
bash-3.2$ ./a.out
./a.out
ep_dbg_getfile(): 0x7fff7082b050
bash-3.2$